Telephone system



May 12, 1942. TOPFER ET AL 2,282,911

TELEPHONE SYSTEM Filed March 30, 1959 4 Sheets-Sheet 1 FEE-.5

Ta I

INVENTORS. HERBERT TOPFER ATTORNEY.

MaylZ, 1942. H. TOPFER ET AL TELEPHONE SYSTEM Filed March so, 1959 4 Sheets-Sheet 2 938. u m H Y .N. UN m .r E E I N P K m UWMN E0 m 0 Z W T R w Tow R E 7 N 5 E ll B H R m A E R w N 93 H E Gm N A 6 Al \aumfi \BU\ Y QQ B 23 E5 t 3x R T K .L I kQ Fey 29 m ou 0 cma fl W Q B HMS L- I b May 12, 1942. H. TCBPFER. ET AL TELEPHONE SYSTEM Filed March so, 1959 4 Sheets-Sheet 3 N U u .f M .m E v Y N. w 0 F K E Um 4 m W m m E O .7 Q W T M U Q 33 1 E A b ibma R m l1 uu E H Nu u H E v 0 Cum I l I Y B S m u c w 2 m NQ Q m ug at SW Es w .6 u T? tow: u \"T 2/ NEW Wm BMEWHN nu l \S Q Q Q L 5% In :2, l 4 2 3 L mN V A 85/ Q :l 01 Q L... m G J @D QGQW L PR UR Yb May 12, 1942. 1-1. TGPFER ET AL.

TELEPHONE SYSTEM Filed March 30, 1939 4 Sheets-Sheet 4 NQ Nm INVENTORSI HERBERT TOPFER ERICH EHRlCKE 45244 ATTORNEY.

vmethod according Patented May 12, 1942 2,282,911 7 TELEPHONE SYSTEM Herbert Tiipfer and Erich Ehricke, Berlin-Sie- .mcnsstadt, Germany, assignors to Fides Gesellschaft fiir die Verwaltung and Verwertung von gewerblichen schrankter Haftung, ration of Germany Application March In German 2 Claims.

The invention relates to a circuit arrangement. .for two conductor two-way junction lines in automatic telephone systems. On the simultaneous seizing of such a junction line from both directions it can happen that one of the two subscribers connected at opposite ends releases the signal for the conversation to begin, e. g. by operating his dial or hanging up his receiver so that the subscriber at the opposite end is charged with a fee in error.

Arrangements for two-way junction lines are already known which by giving preference to a connection in one direction prevent the simultaneous seizing from both directions by allowing the line to be seized from the other direction but disconnecting it so quickly that the above mistake cannot occur. Since however, the known arrangements for bringing about the preferred seizing of the junction line in a particular direction usually have the disadvantage that the seizing operation is prolonged and thus the free selecting period of the selector seizing the junction line is shortened, the invention proceeds by another method in order to avoid the danger of an erroneous metering of a conversation. This to the invention, consists in using for the switching operations to be transmitted back over the junction line in the course of setting up a connection, in particular the signal for the beginning of the conversation, only impulses of such a type, (e. g. different frequency, type of current, voltage) or duration are'used that they cannot be simulated by the impulses serving to transmit the switching operations in the forward direction.

Fig. 1 shows diagrammatically an arrangement for two-way trafiic.

Fig. 2 shows one embodiment of the invention in which different frequencies of current are used for forward and backward signalling.

Fig. 3 shows another embodiment of the invention in which currents of the same frequency, but of diiferent lengths, are used. 1

Fig. 4 shows another embodiment of the in.-

vention in which inductive currents are used for signalling in one direction,

.While alternating current is used for signals in the other direction.

In the arrangement according to Fig. 1 the two exchanges A and B are connected with one another by means of the junction line VL. If the subscriber Tal of the exchange A wishes to make aconnection with the subscriber Th2 of the exchange B then after the subscriber Tal has taken up his receiver his pre-selector VWa. hunts 1939, Serial No. 264,878 y April 12, 1938 l GWa. The group UA by means of the first group selector IGWa' the seizing over the junction line VL to the repeater UB and from this to the second group selector ZGWb of the exchange B connected to the repeater is carried out. The group selector 2GWb is set by the next impulse transmission from the calling subscriber on a free final selector LWb and this is set by the last impulse train on the required subscriber Th2.

A connection in the opposite direction between the subscriber Tbl of the exchange B as calling party and the subscriber Ta2 of the exchange A as called party extends over pre-selector VWb, first group selector lGWb, repeater UB, junction line VL, repeater UA, second group selector I 2GWa, final selector LWa, subscriber T112.

The Figs. 2, 3 and 4 show three different embodiments of the invention in connection with a number of circuits of the repeaters UA and UB at the ends of the junction lines. The circuit details of the repeater are only shown in so far as is necessary for the understanding of the in-v vention. The repeaters UA and UB are completely similar to one another in their circuit connections. Since they serve for outgoing as well as for incoming trafilc, switch means are arranged in each repeater in the part of the line branch incoming to'the group selector and in the part of the branch line extending to a group selector as indicated by a horizontal dotted sepatransmitted backwards, in particular the signal 7 for the metering operationistransmitted with another frequency, e.g. cycles.

In detail the method of working of the arrangement of Fig. 2 is as follows:

On seizing of the repeater UA by means of a previously arranged group selector of the exchange A, the seizing relay Cal is energized: earth, test relay in the group selector, test wiper of the group selector (not shown), conductor 0, contact l8ca2, winding of relay Cal, battery, earth. Relay Cal closes the following circuit for the relay Art; earth, contacts Meal, lZka, winding II of relay Aa, battery, earth. Further by means of the relay Cal the relay We is en-- ergized: earth, contact [1 call, winding of relay Wa, battery, earth. The relay Aa connects the alternating current source Qal of 50 cycles by means of its contacts Aaa and 'laa to the transformer Tm and hence to the junction line VL. The connection of the alternating current is terminated after a short period owing to the operation of relay Ka which disconnect the relay Aa. Relay Ka is energized after the operation of relay Aa in the following circuit: earth, con-. tacts Meal, llaa, winding of the slow relay Ka, battery, earth. The relay Ka operates and holds over its contact lflka independently of relayAa. By the opening of contact l2ka the winding II of relay Aa is disconnected, relay Ad is restored, the alternating current source Qal is disconnected from the junction line and the seizing impulse is thus terminated. The relay Wain the repeater UA disconnects the junction line V'L from the branch line extending to the group selector on its energization by the opening of contact 2wa and two, and by closing the contacts Iwa and wa, switches through to the seized first group selector.

In the repeater UB the alternating current relay Jb2 tuned to 50 cycles is energized for a short while bymeans of the seizing impulse. It should be stated here that in the repeater UB the relay Eb has already been energized in a normally existing circuit previous to the seizing. This normally existing circuit extends over: earth, high resistance winding I of relay Eb, seizing conductor c, principal contact of the connected group selector (not shown), seizing relay of the group selector, battery, earth. The seizing relay of the group selector does not operate in this normal circuit. The seizing impulse for the relay Jb2 therefore extends over the following circuit: secondary windings of the transformer Trb, contacts Nab, 3lwb, 39eb, winding of relay Jb2, contacts 426b, 3 4mb, 33Gb, transformer winding Trb.

Relay Jb2 closes the following circuit for the auxiliary relay Hb: earth, contact 462192, winding of relay Hb, battery, earth. The relay Hb closes the following circuit for the seizing relay Cb2: earth, battery, contacts 41kb, 5412b, winding of relay CbZ, contacts 4901b, 506b, winding II of relay Eb, earth. The relay Cb2 operates in this circuit and holds after the release of relays JM and Hb in the following circuit: earth, winding II of relay Eb, contacts Web, 491%, winding of relay CD2, contacts 54cb2, 53cb2, battery, earth. Relay Cb2 seizes the second group selector not shown, of the exchange B by the direct connection of earth over contact 45cb2 to the c-conductor. Thus in this group selector the seizing relay operates. The relay Eb, whose winding I is short circuited by contact 45cb 2 holds over its winding II in series with the seizing relay CbZ, Relay 0212 further interrupts the incoming test conductor at contact 38cb2 and thus prevents a seizing, by the first group selector of the exchange B, of the repeater UB in the incoming direction. i

The impulses sent outfrom the calling subscriber are taken up by the winding I of relay Jb2 transmits the impulses as earthing impulses over the a-conductor by means of its contact 43hb to the second group selector and final selector. During the impulse selection the slow relay Vb is energized intermittently in the following circuit: earth, contact 52hb, winding of relay Vb, contact 530172, battery, earth. Relay Vb holds during an impulse train. Relay Cb2, which is short circuited intermittently over the contacts l'lhb, 481)?) during an impulse train does not restore.

As soon as the called subscriber has replied the potential is connected to the b-conductor in sation to begin and hence for the metering, by which the relay Sb is energized in the repeater UB1 potential in the final selector, conductor 1) winding of the relay Sb, contact 4211b, earth. The

relay Sb operates'and by means of its contacts 5Isb short circuits the winding II of relay Eb. Relay Eb restores and by means of its contacts Alleb and Meb transmits an alternating current impulse back over the line VL from the alternating current source Qb2. The alternating current from the alternating current source QbZ has a frequency of cycles. The backward impulse is thus completed and after the release of the relay Eb the short circuit for the relay Db is opened at contact 5116b. .Relay Db operates in series with the relay C172 and by means of its contact 49db disc0nnects the relay Sb from the b-conductor. Relay Sb restores. Thus the short circuit for the winding II of the relay Eb is interrupted at the contact 5Isb. Relay Eb operates again. By the opening of the contacts Alleb and 4leb the alternating current source 61112 is disconnected from the junction line VL and the revertive impulse marking the beginning of the conversation is completed. The contacts 3912b and 42eb again set up a connection between the junction line VL .and the outgoing group selector. After the operation of the relay Eb the relay Dbi holds in series with the relays CM and Eb, since the previously existing short circuit at contact 4911b has been opened,

In the repeater UA the alternating current relay Jal which is tuned to 100 cycles is energized in the following circuit by means of the alternating current impulse from the repeater UB:

windings of the transformer Tra, contacts 3aa,

lwa, winding of the relay Jal, contacts Ewa, 8aa, windings of the transformer Tra. The relay Jal closes the following circuit for the auxiliary relay Ha: earth, contact Qzal, winding of relay Ha, battery, earth. Relay Ha closes the following circuit for the relay Ga: earth, contacts l'lcal, lliha, winding of relay Ga, battery, earth. Relay Ga connects over the choke Dr and the contact l9ga the short period metering potential at the b-conductor, whereby in a time zone set associated with the previous group selector, the metering is stored.

When at the end of the conversation the calling subscriber hangs up his receiver the seizing relay Cal is restored in the repeater UA. On the release of the relay Cal the following circuit for the relay Aa is completed: earth, contacts l5cal,

switches the junction line VL back on to the outgoing group selector.

In the repeater UB the relay .1172 is energized by means of the long release impulse and also the relay-I-Ib. Relay Hb energizes the relay Vb. Then over the contacts 41hb, 48fub the seizing relay C212 is short circuited .for a long period and restores. After the release of the relay Cb-2 the relays Eb and Db also restore. -By the release of the rela C172 a seizing circuit to the outgoing group selector is opened at the contact 450122 and thus its release and the release of the next selector is initiated. As soon as the second group has reached its normal position the relay Eb operates over the c-conductor with its winding I. The repeaters are thus prepared for seizing again.

. On a connection from exchange B to exchange A the same switching operations occur as in the previously described connection. When the repeater UB is seized over a first-group selector of the exchange B by means of a calling subscriber the seizing relay Cbl is operated over the incoming c-conductor. This efiects the transmission of a short seizing impulse of 50 cycles from the alternating current source Qbl over the junction line. Relay Cbl thus controls a relay Ab, over a winding not shown, which with its contacts 3lab and 32ab connects alternating current to the junction line. The alternating current-impulse is taken up in the repeater UA from the alternating current receiving relay Ja2 tuned to 50 cycles. Relay Ja2 energizes the seizing relay Ca2 not shown, and this seizes an outgoing second group selector by means of its contact The selecting impulses from the calling sub- I .scriber are taken up from the winding of the relay Ab on the a-conductor and transmitted directly over the junction line as alternating current impulses of 50 cycles. In the repeater UA they. are taken up by the relay JaZ and transmitt'ed-as earthing impulses over the a-conductor. When the called subscriber in the exchange A replies the relay Ea is restored after a while and by means of its contacts Zlea and Hal transmits an alternating current impulse of 100v cycles from the alternating current source QaZ back over the junction'line VL to the repeater UB. Here this is taken up from the alternating current relay Jbl tuned to 100 cycles. Relay Jbl switches over this impulse which marks the initiating of metering in that it connects potential at the b-COIldLlCtOI for a short period back to the calling subscriber. The release is per-' formed by means of a long alternating current impulse which is transmitted from the repeater UB on the hanging up on the part of the calling subscriber.

If the repeaters UA and UB should simultaneously seize the line from opposite directions then by means of impulses in the opposite directions which for example can arise so that one of the subscribers is subsequently selected or hangs up his receiver disturbances in particular erroneous initiations of metering operations do not occur. In such a case on the one hand from the two repeaters the Ga and Au operate.

contact 5cal, winding of the relay lowing circuit: earth, contacts [20111,

junction lines are switched through to the alternating current relays Jal or ,J b2 tuned to .100 cycles, and; on the other hand the impulses transmitted from the two .opposite subscribersare only transmitted with a "frequency of 5 0 cycles whereby the alternating current relays are not operated.

Fig. 3 showsan embodiment ofthe invention .in which all the signals, the forwardly directed as well as the revertively transmitted signals, are transmitted withthe same kind of current, e. g.

alternating current of the same freq'uencyiover thegguarded line but have ,difierent lengths. yThus forthe forwardly directed switching operations of seizing and. selection short impulses are transmitted, and'for the release a long impulse, while, for the. signal to be transmitted back for the metering a so-called half-length impulse is used. These half-length impulses are longer than the impulses for transmission and shorter than the release impulse so that when the two repeatersare connected together neither on the.

ation occur ata subscribersstation. I The method of-working of the arrangement in Fig. 3 is as follows: on the seizing of the reselection nor on the release can a metering operpeater UA over .afirst group selector of the ex- 1 change A the seizing relay Cal operates, .over the c-Conductor in the following circuit: earth,

test relay in the first group selector, test wiper of the first group selector (not shown), c-conduotoncontact 3lca2, winding of relay Cal,bat-

tery, earth. Relay Cal closes the following circuit for the relays Ga and Aa: earth, contact l2cal, winding I of relay Ga, .contact Iilna,

winding II of relay Aa, battery, earth. The relays Relay Ga holds in the 'following circuit: earth, contact Seal, winding I of relay Ga, contact 3|ga, resistance Wi, battery, earth. Further the relay Wa is energized: earth, Wa, battery, earth. The relay Wu. connects the junction line at the contacts 2310a and 251m through to the incoming group selector. The relay Aa transmits a short alternating current impulse of 50 cycles from the alternating current source WQa by means of its contacts 28cc and 29m for seizing over the junction line VL. The seizing impulse ,is so completed that after the energization of the relay Aa the relays Ka and Na are energized. Relay Na thereupon interrupts the circuit for the relay Ad. The circuit formed for relay Ka at the energization of. relay Aa is as follows: earth, contacts of relay Ka, battery, earth. Relay Kaholds independently of relays Aa and Na in the follha, 47cc, winding of relay Ka, battery, earth. Relay Ka further closes the following circuit for the relay Na: earth, contacts 5cal, 970a, winding of relay Na, battery, earth. Relay Na interrupts the circuit for the relay Aa by opening contact Iona. Relay Na holds independently of relay Ka in the following circuit: earth, contacts 5cal, winding of relay Na, battery, earth. r

In the repeater UB the alternating current relay Jb2 is energized by means of the seizing impulses. It should be inserted here that the relay Eb has already been energized previous to', the seizing of the repeater in the normal circuit extending over its high resistance winding I and the c-conductor extending. to the outgoing second group selector. The relay Jb2 is thus energized by means of the seizing impulse in the following ci w i s. sfithe r pe ter ,Trb,

l2ca, 311a, Zna, winding relay CbZ: earth, battery, contacts 54kb, 640b,

winding of the relay CbZ, contacts lildb, 50eb, winding II of the relay Eb, earth. After the release of relay Hb the relay 'Cb2 holds over its contacts 56cb2 and-55cb2. Relay CbZ interrupts the incoming test conductor at contact 48cb2and thus prevents the seizing of the repeater UB in the incoming direction. By means of its contact 63cb2 the relay CbZ connects direct earth to the outgoing c-conductor and thus seizes the connected second group selector whose seizing relay is now energized. The relay Eb whose winding I is short circuited by means of contact 63sb2 holds overthe winding II in series with the seizing relay Cb2.

The impulses which are transmitted from the calling subscriber are taken up by the winding I of the relay Ad of the repeater UA connected to the a-conductor. Relay Aa transmits these by means of its contacts 28cc and 29041 directly as alternating current impulses over the junction line. They are taken up in the repeater UB by the relay Jb which energizes the relay Hb intermittently. Relay Hb transmits the received impulses by means of its contact Blhb as earthed impulses over the a-conductor to the succeeding selector. During the selection slow relay VB is also energized intermittently: earth, contact 5211b, winding of relay Vb, contact 550112, battery, earth. The relay Vb holds during an impulse train. Relay CD2, which is short circuited during the impulse selection over the contacts 5471b, 53th is thereby not restored.

When the required subscriber replies, potential is connected to the b-conductor in the final selector which brings about the operation of relay Sb in the repeater UB1 potential in the final selector, b-conductor, winding of relay Sb, contacts 62 db, earth. The relay Sb operates and short-circuits the winding II of relay Eb. Relay Eb restores and by means of its contacts 5Beb and 59eb transmits an alternating current impulse from the alternating current source WQb back over the line VL to the repeater UA as a signal for the conversation to begin. Relay Eb opens the short circuit for relay Db on its release by means of contact 50eb. Relay Db operate in series with relay C172 and holds after the energizing of relay Eb, since the previously existing circuit at contact 5Idb is finally opened. Relay Db disconnects the relay Sb from the bconductor at contact SZdb. Relay Sb restores, and the short circuit for the winding II of relay Eb is interrupted at contact 48sb. Relay Eb operates. In this way the revertive impulse which constitutes the signal for initiation of metering is completed. The duration of the revertive impulse is essentially determined by the release period of the slow relay Sb. This is so arranged that the length of the revertive impulse lies between that of the short seizing impulse or selecting impulse and that of the long release impulse transmitted at the termination of the connection.

In the repeater UA by means of the halflength revertive impulse for metering the relay Jal is energized: Winding of the relay Jal, contacts 2510a, 30aa, windings of the transformer Tra. Relay Jal closes the following circuit for the relay Ha: earth, contact llial, winding of the tor.

relay Ha, battery, earth. The relay Ha short circuits the winding II of relay Ga over contact 67m. This short circuit continues for a sufficient period to bring the relay Ga to restore. The duration of this impulse is not suflicient, however, to bring the relay Ka to restore, in spite of which after the release of relay Jd the holding circuit of relay Ka is interrupted at-the contacts the and 19a. Before the relay Ka has restored the holding circuit is already completed by means of the contact lha of the restored relay Ha. A further operation of the relay Ga after the release of the relay Ha is prevented in that the contact 3lya interrupts the energizing circuit for the relay Ga. After the release of the relays Ga and Ha metering potential is connected at the b-conductor back to the calling subscriber: earth, battery, choke, Dr, contacts Hiya, l5ha, tlflka, b-conductor back to the first group selec- The release of the connection takes place when the calling subscriber hangs up. Thus the seizing circuit extending from the first group selector is interrupted so that the seizing relay Cal in the repeater is restored. After the release of the relay Cal the relay Aa is energized in the following circuit: earth, contacts l3cal, llna, winding II of relay Aa, battery, earth. The relay Aa transmits a long alternating current impulse by means of its contacts 2811a and 2911a in order to release the junction line. The duration of the release impulse is determined by the release peri-- 0d of the slow relay Na. Its release period amounts to about 200 ms. The holding circuit of the relay Na is interrupted after the release of relay Cal at contact 5cal. Relay Na opens the energizing circuit of winding II of relay Aa at'contact Hna. Relay Aa restores and thus completes the release impulse. By the restoration of relay Cal the holding circuit for the slow relay Ka is also opened. This relay restores but its release period is shorter than that of relay Na. The reason for this will be explained later.

In the repeater UB by means of the long release impulse the relay J 172 is energized for a long period. Relay Jb2 energizes the relay Hb for a long period. Relay Hb energizes the relay Vb. Now over the contacts 547th and 5322b the seizing relay Cb2 is short circuited for a long period and thus restores. After the release of the relay Hb the relays Db, Eb and Vb also restores. The relay Cb2 interrupts the seizing circuit to the outgoing group selector at contact 630122 and thereby initiates its release and that of the next selec- If the outgoing selector has reached its normal position the high resistance winding I of relay Eb operates over the outgoing c-conductor again and prepares the repeater UB for seizing again.

The setting up of a connection in the direction from the exchange B to the exchange A requires no further elucidation. The same switching operations occur as described previously. The repeater UB when it is seized by an incoming group selector by means of the relays Cbl and Ab transmits a short seizing impulse from the alternating current source WQb over the junction line VL to the repeater UA. Here this is taken up by the relay Ja2 and the energizing of the seizing relay Ca! not shown is effected.

The impulses from the calling subscriber are received by the relay Ab and transmitted as alternating current impulses over the junction VL. In the repeater UA the relay Ja2 converts the impulses to earthing impulses on the a-conductor.

subscriber by connecting metering potential to:

the b-conductor.

The release takes place when the calling subscriber hangs up and is performed by the transmission of a long alternating current impulse over the junction line.

The previously described embodiment also prevents an erroneous metering being charged to one of the subscribers when the junction line is seized simultaneously from opposite directions.

Thus when one of the subscribers connected tolines at opposite ends for example the subscriber of the exchange B transmits impulses after the seizing of the repeater UB the relays J at and Ho areintermittently energized for brief periods by the short alternating current impulses extending from the repeater UB to the repeater UA. Over the contact 6h the relay Ga is short circuited but the short circuit does not last sufiiciently long to bring the relay to restore. hangs up whereby a long release impulse is transmitted over the junction line from the repeater UA the relays J al and Ha in the repeater UA are energized for a long period. Relay Ha short circuits the winding II of relay Ga over contact Gha. Relay Ga restores. Further by means of the long'impulse after the release of the relay Ga the holding circuit of the relay Ka'is opened at contact lha until the relay Ka whoserelease period is shorter than the duration of the long release impulse, has restored. When the relays Ha and Ga restore at the end of the release impulse the metering circuit to the calling subscriber can no longer be completed since a connecting of metering potential to the b-conductor is rendered impossible by the opening of contact Mica.

Fig. 4 shows an arrangement in which an inductive direct current impulse is provided for the signal in the direction from the calling to the called subscriber, and an alternating current impulse for the signal for metering in the opposite direction. Thus in the case of two-way traffic when the repeaters at both ends of the line are connected, no metering impulse can occur since the inductive impulse is not sufiicient to operate the alternating current relay which initiates the metering.

The method of working of the arrangement n Fig. 4 is as follows: When the repeater UA is seized by a group selector of the exchange A in the incoming direction the seizing relay Cal operates over the test conductor of the preceding group selector: earth, test relay in the preceding group selector, test wiper of the preceding group selector, c-conductor contact 33ca2, winding of relay Cal, battery, earth. Relay Cal closes the following circuit for relay Xa: earth, contacts Hcai, lzcal, winding of relay Xa, battery, earth. Relay Ca! further closes the following circuit for the relay Wa: earth, contact lilcaL winding of When the subscriber v transformer Tfa battery, earth. Relay Au. completes the follow.-'

ing direct current circuit over the winding Iof the transformer Tia: earth, contact Slaa, winding I of the transformer Tfa, battery, earthr Thus in the winding II of the transformer, animpulse is induced in one direction which is,

marked as a positive direction. From the secondary winding of the transformer Tfa this impulse is transmitted in the following circuit to the junction line VL: winding II of the transformer Tfa, contact waa', primary windings of the transformer Tm; contact am, winding II of the transformer Tfa. j After the operation of the relay Act the following circuit is completed for the relay Ma: earth, contact Had, winding of the relay Ma, battery, operation of the relay Aa' the following circuit is set up for the; relay Da:. Earth, contacts Ira, 3aa, winding of =relay. Da, battery,learth. The relay Da holds over its contact ,2cla independentlyof the relay Aa. Bymeans of the operation of the relay Da the energizing circuit for the relay Ad is interrupted at contact Eda. In this way the direct current circuit over the winding I .of the is first interrupted and an impulse in the negative direction induced in the winding II of the transformer Tfa which extends over contact 2'Ima, primary' windings of the transformer Tm and contact 29ma, back to winding II of the transformer Tfa. Correspondingly an impulse in" the negative directionalso extends over the junction line VL.

In the repeater UB there operates the polarized accepting relay-Pb due to the positive inductance impulse and the relay P closes its contact 6679b. .Relay Eb has already been seized the' relay. Wu, battery, earth. Relay Wa by previous to the energization in the normal circuit over the seizingconducto'r extending to the outgoing group selector.. The circuit for the relay Pb is as follows: windings of the transformer Trb, contacts Tlab, T3mb, 5lwb, 63eb, winding of the polarized relay Pb, contacts 656b, 53wb, windings of the transformer Trb. Over contact 661217 the auxiliary relay Hb is energized. By means of relay Hb the following, energizing circuit is completed for the seizing relay Cb2:' earth, battery, contacts 5771b, 7312b, winding of the relay Cb2, contacts 59db, Web, winding II of relay Eb, earth. By means ofthe negative induction impulse following on thepositive impulse the polarized relay Pb sets back its armature for a short period. The relayHb also restores. After the release of the relay E1) the relays CbZand Eb are maintained energized in the following circuit: earth,'windingII of relay Eb, contacts 602b,

sistance winding I over the winding II in series with the seizing relay Cb2.

The impulses transmitted from the calling subscriber are received in the repeater UA by the impulse accepting relay Aa connected to the a-conductor and transmitted alternatively as positive and negative inductance'impulses'overthe'junction line 'VL'. Relay Aa thereby closes and'opens alternately a direct current circuit over the winding I of thetransformer Tfa, whereby impulsesin alternate directions are induced earth. Further after the Relay EU is maintained energized after the short circuit of its high rein the winding II of this transformer.

Further the relay Aa energizes the relay Ma on each impulse over contact llaa. Relay Ma holds over its contacts Zlma and 29ma in the impulse trans,-

mitting circuit closed during the negative impulses.

In the repeater UB the impulses are transmitted by the auxiliary relay I-Ib. The relay Hb transmits these by means of its contact 'Ilhb as earth impulses over the a-conductor to the next selector while during the impulse transmission over contact 54hb a slow relay Vb is ener- Y gized intermittently. Relay Vb holds during an impulse train. The seizing relay Cb2 short circuited intermittently over the contact 580D and Slhb holds during the impulse selection.

When the required subscriber replies potential is connected to the b-conductor in the selector by which the relay Sb in the repeater UB is operated: potential in the final selector, b-conductor, winding of the relay Sb, contact 69db, earth. The relay Sb operates and short circuits the winding II of the relay Eb over contact Slsb. Relay Eb restores and by means of its contact 62eb and (Web connects the alternating current source WQb to the junction line VL. This alternating current revertive impulse marking the metering apparatus is thus completed. After the release of the relay Ab, the short circuit at contact lilleb is opened and the relay Db operates in series with the relay CbZ. Relay Db disconnects the relay Sb from the b-conductor by the opening of the contact 69db. Relay Sb restores. After the opening of the short circuit for the winding 11' of the relay Eb at contact Slsb the relay Eb Operates again. Relay Eb opens its'contacts 6261), Mob and closes its contacts 63eb, 65eb, whereby the revertive impulse is completed. After the operation of the relay Eb the relay Db holds in series with the relays CM and Eb, since the previously existing short circuit at the contact 59db is now finally interrupted. Relay Sb is connected in bridge across the outgoing talking conductor after the operation of the relays Eb and Db over the contacts Hleb and BBdb. It then serves as a monitoring relay when the called subscriber hangs up. 7

In the repeater UA by means of the revertive impulse marking the initiation of metering the alternating current relay Ja tuned to cycles is energized in the following circuit: transformer windings Tra, contacts 2Baa, 25ma, 23wa, winding of the relay Ja, contact 32wa, transformer windings Tra. Relay Ja completes the following circuit for relay Ha: earth, contacts l8cal, the, winding of the relay Ga, battery, earth. Relay Ga connects metering potential for a short period over the choke Dr and contact lfiga to the b-conductor whichin the present case is stored in a time zone set associated with the seizing group selector. After the completion of the impulses the relays J a, Ha, Ga again restore.

The release of the connection takes place when the calling subscriber hangs up. Thus the test conductor in the seizing groupselector is interrupted and the relay Cal of the repeater UA is restored. After the release of the relay Cal the following circuit is completed for the relay Aa: earth, contacts Hlcai, Ada, winding of the relay Aa, battery, earth. Relay Aa again induces a positive impulse in the winding II of the transformer Tfa which extends over the junction line VL to the repeater UB. The'relay Aa'only, re-

store's after a long period and thereby transmit-s an induction impulse of negative direction over th junction line VL. By means of the release of relay CAI the circuit for the relay Xa is in--' terrupted at the contacts Neal and IZcal. The.

The release impulse consists of a positive and negative induction impulse with a long pause. In the repeater UA by means of'the release of the relay Cal the relay Wa is further brought torestore. Relay Wa switches over the connection again on to the branch'leading to the outgoing group selector.

In the repeater UB by means of the positive inductive impulse the relay Pb is energized which operates the relay'Hb. The relay Hb short cir-.

cuits the relay GM for a long period over contacts 5'lhb and 58 vb. Relay Cb2 restores thereby. After the. release of the relay Hb the relays Db and Eb also restore. The release of the relay C172 by disconnecting the feeding potential at contact 6'lcb2 from the seizing conductor initiates the release of the next selector. After the return to normal of the outgoing group selector the relay Eb operates again over the high resistance winding I and the seizing conductor 0 in the normal position whereby the repeater UB is prepared for seizing again. i

What is claimed is:

1. In a telephone system, a two way two conductor trunk line, means for seizing said trunk line' and automatic switches for extending connections thereover in either direction, means on each end of said trunk line responsive to impulses from a calling subscriber when the trunk line is seized for transmitting impulses of alternating current of one frequency over said trunk line to operate said switches to extend connections thereover to called subscribers, and means on each end of said trunk line operated when a called subscriber responds to the completion of a connection thereover for transmitting an impulse of alternating current of another frequency over said trunk line.

2. In a telephone system, a two way two conductor trunk line, automatic switches operated by a calling subscriber to seize said trunkline at either end and extend connections thereover via other automatic switches, means on each end of the trunk line responsive to seizure thereof by certain of said switches for transmitting alternating current of one frequency over the trunk line to control automatic switches thereover and responsive to impulses from the calling subscriber to transmit impulses of said frequency over the trunk line to operate the seized switches to extend a connection therefrom to a called subscriber, and means on each end of the trunk line operated when a called subscriber responds to the completion of an extended connection thereto for transmitting an impulse of alternating current of another frequency over the trunk line in the direction of the calling subscriber.

HERBERT ToPFER. ERICH EHRICKE. 

